Vardaan Learning Institute

Why it cannot form ionic bonds:

1. It cannot gain 4 electrons to form $\text{C}^{4-}$: Carbon has only 6 protons in its nucleus. It is extremely difficult for a tiny nucleus with 6 protons to hold onto 10 electrons (6 original + 4 gained) due to massive inter-electronic repulsion.
2. It cannot lose 4 electrons to form $\text{C}^{4+}$: Removing 4 electrons from a tiny carbon atom requires an enormous, practically unavailable amount of ionisation energy to overcome the strong electrostatic attraction of the nucleus.

Therefore, carbon overcomes this energy barrier by sharing its 4 valence electrons with other atoms, forming covalent bonds instead.

Electron-dot structures:

1. Hydrogen ($\text{H}_2$ - Single Bond): Each H atom shares 1 electron to complete its duplet. $$\text{H}^{\bullet} + \cdot\text{H} \rightarrow \text{H} : \text{H} \rightarrow \text{H}-\text{H}$$
2. Oxygen ($\text{O}_2$ - Double Bond): Each O atom (2, 6) shares 2 electrons to complete its octet. $$\text{:}\ddot{\text{O}}\text{:} + \text{:}\ddot{\text{O}}\text{:} \rightarrow \text{:}\ddot{\text{O}}\text{::}\ddot{\text{O}}\text{:} \rightarrow \text{O}=\text{O}$$
3. Nitrogen ($\text{N}_2$ - Triple Bond): Each N atom (2, 5) shares 3 electrons to complete its octet. $$\text{:}\dot{\text{N}}\text{:} + \text{:}\dot{\text{N}}\text{:} \rightarrow \text{:N:::N:} \rightarrow \text{N}\equiv\text{N}$$

Electron-dot structure: $$\begin{array}{ccc} & \text{H} & \\ & \bullet & \\ \text{H} \bullet & \text{C} & \bullet \text{H} \\ & \bullet & \\ & \text{H} & \end{array} \rightarrow \begin{array}{ccc} & \text{H} & \\ & \lvert & \\ \text{H} & - \text{C} - & \text{H} \\ & \lvert & \\ & \text{H} & \end{array}$$ Valencies: The valency of carbon is 4 (tetravalent), and the valency of hydrogen is 1 (monovalent).

1. Water ($\text{H}_2\text{O}$): Oxygen shares 2 electrons with 2 H atoms, leaving 2 lone pairs. $$\text{H} \cdot \, \cdot \ddot{\text{O}} \ddot{\cdot} \, \cdot \text{H} \rightarrow \text{H}-\ddot{\text{O}}-\text{H}$$
2. Ammonia ($\text{NH}_3$): Nitrogen shares 3 electrons with 3 H atoms, leaving 1 lone pair. $$\begin{array}{ccc} & \text{H} & \\ \text{H} \cdot & \ddot{\text{N}} & \cdot \text{H} \end{array} \rightarrow \begin{array}{ccc} & \text{H} & \\ \text{H} & - \ddot{\text{N}} - & \text{H} \end{array}$$
3. Carbon dioxide ($\text{CO}_2$): Carbon shares 4 electrons (2 pairs with each oxygen atom) to form two double bonds. $$\text{:}\ddot{\text{O}}\text{::C::}\ddot{\text{O}}\text{:} \rightarrow \text{O}=\text{C}=\text{O}$$

Why low melting/boiling points: Overcoming these weak intermolecular attractions to melt or boil the substance requires very little thermal energy. (Contrastingly, ionic compounds are held by exceptionally strong electrostatic attractions throughout a massive 3D crystal lattice).
Why poor conductors: Covalent bonds involve the local sharing of electrons between atoms. All valence electrons are locked inside these bonds, and there are no free-moving electrons or mobile ions in either solid, liquid, or dissolved states to carry electric charge.

How it leads to stability: By sharing, both atoms are able to count the shared electrons as part of their own valence shells. This allows each atom to complete a stable, lowest-energy duplet (for hydrogen) or octet (for other non-metals) configuration, matching the highly stable electron configuration of noble gases.

Property	Diamond	Graphite
Structure	Rigid, 3D giant tetrahedral network. Each carbon bonded to 4 others.	Flat, 2D hexagonal layered sheets. Each carbon bonded to 3 others.
Hardness	Extremely hard. The hardest natural substance known.	Soft, slippery, and greasy to touch.
Conductivity	Poor electrical conductor (no free electrons).	Excellent electrical conductor (due to 1 free delocalised electron per atom).

Buckminsterfullerene ($\text{C}_{60}$):

• Structure: It contains 60 carbon atoms arranged in a spherical shape resembling a soccer ball. The cage consists of 20 hexagons and 12 pentagons.
• Chemical Properties: It is relatively stable at room temperature but undergoes addition and substitution reactions under specific conditions. Unlike diamond and graphite, it is slightly soluble in organic solvents like toluene.

• Why Diamond has high melting point: In diamond, all carbon atoms are locked in a strong, rigid, three-dimensional tetrahedral covalent network. Melting diamond requires breaking millions of these strong C-C covalent bonds, which requires a massive amount of thermal energy (~3550°C).
• Why Graphite is a dry lubricant: Graphite consists of parallel hexagonal layers of carbon atoms. While the bonding within each layer is strong covalent, the different layers are held together only by very weak van der Waals forces. When shear force is applied, these layers easily slide over each other, making graphite slippery and greasy.

1. Catenation: The unique ability of carbon atoms to form stable, strong covalent bonds with other carbon atoms, yielding exceptionally long straight chains, branched networks, and rings.
2. Tetravalency: Since carbon has a valency of 4, it is capable of bonding with four other monovalent atoms, or forming double and triple bonds with oxygen, nitrogen, sulphur, and other carbon atoms.

Why carbon shows exceptionally high catenation: The size of a carbon atom is extremely small. Because of its tiny atomic size, the shared electron pair of the C-C bond is strongly attracted by both nuclei, making the C-C bond exceptionally strong and stable (bond energy ~348 kJ/mol). Silicon also shows catenation, but because silicon atoms are larger, the Si-Si bond is much weaker, and chains beyond 7 or 8 atoms are highly unstable.

• Saturated compounds: Compounds where all carbon atoms are linked together only by single covalent bonds (alkanes, e.g., ethane). They are less reactive.
• Unsaturated compounds: Compounds containing at least one double or triple covalent bond between carbon atoms (alkenes and alkynes, e.g., ethene, ethyne). They are highly reactive.

Structural formulas:

• Ethane ($\text{C}_2\text{H}_6$): $$\text{H}_3\text{C}-\text{CH}_3$$
• Ethene ($\text{C}_2\text{H}_4$): $$\text{H}_2\text{C}=\text{CH}_2$$

Isomers of Pentane ($\text{C}_5\text{H}_{12}$):

1. n-Pentane (straight chain): $$\text{CH}_3-\text{CH}_2-\text{CH}_2-\text{CH}_2-\text{CH}_3$$ IUPAC Name: Pentane
2. Isopentane (branched chain): $$\begin{array}{c} \text{CH}_3-\text{CH}-\text{CH}_2-\text{CH}_3 \\ \lvert \\ \text{CH}_3 \end{array}$$ IUPAC Name: 2-Methylbutane
3. Neopentane (cross-branched chain): $$\begin{array}{cc} & \text{CH}_3 \\ & \lvert \\ \text{CH}_3 - & \text{C} - \text{CH}_3 \\ & \lvert \\ & \text{CH}_3 \end{array}$$ IUPAC Name: 2,2-Dimethylpropane

1. Propane:
   • Molecular Formula: $\text{C}_3\text{H}_8$
   • Structural Formula: $\text{CH}_3-\text{CH}_2-\text{CH}_3$
2. Butyne:
   • Molecular Formula: $\text{C}_4\text{H}_6$ (using general formula $\text{C}_n\text{H}_{2n-2}$)
   • Structural Formula: $\text{HC}\equiv\text{C}-\text{CH}_2-\text{CH}_3$ (But-1-yne)
3. Benzene:
   • Molecular Formula: $\text{C}_6\text{H}_6$
   • Structural Formula: A closed ring of 6 carbon atoms with alternating single and double bonds: $$\text{C}_6\text{H}_6 \text{ (Ring structure with alternating double bonds)}$$

Three characteristics:

1. All members can be represented by the same general molecular formula (e.g., $\text{C}_n\text{H}_{2n+2}$ for alkanes).
2. They exhibit very similar chemical properties because they contain the same functional group.
3. Their physical properties (boiling/melting points, density) show a gradual, regular progression as molecular mass increases.

Why mass differs by 14 u: The atomic mass of Carbon is 12 u, and Hydrogen is 1 u. The mass of one $-\text{CH}_2-$ unit is: $$\text{Mass} = 12\text{ u (C)} + 2 \times 1\text{ u (H)} = 14\text{ u}$$ First three members of Alkanes homologous series:

1. Methane ($\text{CH}_4$, mass = 16 u)
2. Ethane ($\text{C}_2\text{H}_6$, mass = 30 u)
3. Propane ($\text{C}_3\text{H}_8$, mass = 44 u)

• Cyclohexane ($\text{C}_6\text{H}_{12}$): A ring of 6 carbon atoms where each carbon is bonded to adjacent carbons by single bonds and to two hydrogen atoms.
  Classification: It is a saturated cyclic hydrocarbon.
• Benzene ($\text{C}_6\text{H}_6$): A ring of 6 carbon atoms containing alternating single and double bonds.
  Classification: It is an unsaturated cyclic (aromatic) hydrocarbon.

Reason for physical gradation: Larger molecular mass and greater surface area increase the strength of intermolecular van der Waals forces of attraction between the molecules. Since stronger intermolecular attractions require more thermal energy to break, physical properties like melting point, boiling point, and density show a regular increase down the series, while solubility in water decreases.

Electron-dot structure: $$\text{H} \cdot : \text{C} ::: \text{C} : \cdot \text{H}$$ Structural formula: $$\text{H}-\text{C}\equiv\text{C}-\text{H}$$ Type of bond: A triple covalent bond (sharing of 3 pairs of electrons) exists between the two carbon atoms.

1. Alkanes (General Formula: $\text{C}_n\text{H}_{2n+2}$):
   • $\text{C}_3\text{H}_8$ (Propane)
   • $\text{C}_2\text{H}_6$ (Ethane)
2. Alkenes (General Formula: $\text{C}_n\text{H}_{2n}$):
   • $\text{C}_4\text{H}_8$ (Butene)
   • $\text{C}_3\text{H}_6$ (Propene)
3. Alkynes (General Formula: $\text{C}_n\text{H}_{2n-2}$):
   • $\text{C}_5\text{H}_8$ (Pentyne)

Four oxygen-containing functional groups:

1. Alcohol: $-\text{OH}$ (hydroxyl group)
2. Aldehyde: $-\text{CHO}$ (formyl group, contains carbonyl attached to hydrogen)
3. Ketone: $-\text{CO}-$ (carbonyl group, positioned within carbon chain)
4. Carboxylic Acid: $-\text{COOH}$ (carboxyl group)

First, identify the longest continuous carbon chain to determine the parent alkane name.

1. Halogen: Named as a prefix. Add "chloro-" or "bromo-" before the parent alkane name, specifying the carbon position if necessary (e.g., Chloropropane).
2. Alcohol: Replace the ending "-e" of the parent alkane with the suffix "-ol". Specify the carbon position number if chain is 3 or more carbons (e.g., Propan-1-ol).
3. Carboxylic Acid: Replace the ending "-e" of the parent alkane with the suffix "-oic acid" (e.g., Propanoic acid). The acid carbon is always numbered as Carbon-1.

1. $\text{CH}_3-\text{CH}_2-\text{CH}_2-\text{OH}$:
   IUPAC Name: Propan-1-ol (3 carbons, single bonds, alcohol group).
2. $\text{CH}_3-\text{CH}_2-\text{CHO}$:
   IUPAC Name: Propanal (3 carbons total, aldehyde carbonyl group).
3. $\text{CH}_3-\text{CO}-\text{CH}_3$:
   IUPAC Name: Propanone (3 carbons, ketone carbonyl group in the middle).
4. $\text{CH}_3-\text{CH}_2-\text{COOH}$:
   IUPAC Name: Propanoic acid (3 carbons, carboxylic acid group).

Examples: Oxygen ($\text{O}$) in alcohols/acids, and Chlorine ($\text{Cl}$) in alkyl halides.

1. First Member (1 Carbon):
   • IUPAC Name: Methanal (Common name: Formaldehyde)
   • Molecular Formula: $\text{HCHO}$
   • Structural Formula: $\text{H}-\text{C}(=\text{O})-\text{H}$
2. Second Member (2 Carbons):
   • IUPAC Name: Ethanal (Common name: Acetaldehyde)
   • Molecular Formula: $\text{CH}_3\text{CHO}$
   • Structural Formula: $\text{CH}_3-\text{C}(=\text{O})-\text{H}$

1. Propanone: $$\text{CH}_3-\text{CO}-\text{CH}_3$$
2. Butanal: $$\text{CH}_3-\text{CH}_2-\text{CH}_2-\text{CHO}$$
3. Bromopentane: $$\text{CH}_3-\text{CH}_2-\text{CH}_2-\text{CH}_2-\text{CH}_2-\text{Br}$$
4. Hexanoic acid: $$\text{CH}_3-\text{CH}_2-\text{CH}_2-\text{CH}_2-\text{CH}_2-\text{COOH}$$

Why Propanone is the first member: A ketone carbonyl group must be bonded to two other carbon atoms on either side. Therefore, the minimum number of carbon atoms required to form a ketone molecule is three. A one-carbon or two-carbon ketone cannot exist. Thus, propanone ($\text{CH}_3-\text{CO}-\text{CH}_3$, containing 3 carbons) is the first and simplest member of the ketone homologous series.

1. $\text{C}_2\text{H}_5\text{OH}$ $\rightarrow$ Alcohol ($-\text{OH}$ group)
2. $\text{CH}_3\text{CHO}$ $\rightarrow$ Aldehyde ($-\text{CHO}$ group)
3. $\text{CH}_3\text{COCH}_3$ $\rightarrow$ Ketone ($-\text{CO}-$ group)
4. $\text{CH}_3\text{COOH}$ $\rightarrow$ Carboxylic acid ($-\text{COOH}$ group)

Balanced chemical equations:

1. Methane gas: $$\text{CH}_4(g) + 2\text{O}_2(g) \rightarrow \text{CO}_2(g) + 2\text{H}_2\text{O}(g) + \text{Heat } \& \text{ Light}$$
2. Ethanol liquid: $$\text{C}_2\text{H}_5\text{OH}(l) + 3\text{O}_2(g) \rightarrow 2\text{CO}_2(g) + 3\text{H}_2\text{O}(g) + \text{Heat } \& \text{ Light}$$

Nature of process: Combustion is highly exothermic because a large amount of heat and light energy is liberated during the process.

When do saturated hydrocarbons burn with a sooty flame? Saturated hydrocarbons burn with a yellow, sooty flame if the air supply is limited/blocked, which prevents complete oxidation and causes incomplete combustion.

Equation for oxidation of ethanol: $$\text{CH}_3\text{CH}_2\text{OH}(l) \xrightarrow{\text{Alkaline } \text{KMnO}_4 + \Delta} \text{CH}_3\text{COOH}(aq)$$ Or using Acidified $\text{K}_2\text{Cr}_2\text{O}_7$.

Two strong chemical oxidizing agents:

1. Alkaline Potassium Permanganate ($\text{KMnO}_4$)
2. Acidified Potassium Dichromate ($\text{K}_2\text{Cr}_2\text{O}_7$)

Hydrogenation of Vegetable Oils: Vegetable oils contain unsaturated liquid carbon chains. When heated with hydrogen gas in the presence of a catalyst, they are converted into solid, saturated fats (vegetable ghee): $$\text{R}_2\text{C}=\text{CR}_2 + \text{H}_2 \xrightarrow{\text{Nickel (Ni) Catalyst, } \Delta} \text{R}_2\text{CH}-\text{CHR}_2 \text{ (Saturated fat)}$$ Catalyst used: Finely divided Nickel (Ni) or Palladium (Pd).

Therefore, nutritionists recommend consuming unsaturated fatty acids (vegetable oils) over saturated fats for good cardiovascular health.

Balanced chemical equation (Methane with Chlorine): $$\text{CH}_4(g) + \text{Cl}_2(g) \xrightarrow{\text{Sunlight / UV}} \text{CH}_3\text{Cl}(g) + \text{HCl}(g)$$ Why called substitution: Saturated alkanes are unreactive and cannot undergo addition. In the presence of sunlight, highly reactive chlorine radicals substitute or displace one of the hydrogen atoms of methane, forming chloromethane ($\text{CH}_3\text{Cl}$) and hydrogen chloride.

Procedure & observations: Add a few drops of orange-red bromine water to separate test tubes containing cooking oil and melted butter.

1. Cooking Oil (Unsaturated): The orange-red colour of bromine water is decolourised instantly. This is because the unsaturated carbon chains undergo an addition reaction, adding bromine atoms across the double bonds: $$\text{Cooking Oil (Unsaturated)} + \text{Br}_2\text{ (Orange-red)} \rightarrow \text{Dibromo addition product (Colourless)}$$
2. Butter (Saturated): The orange-red colour of bromine water does not fade and remains unchanged because saturated fats do not undergo addition reactions.

• It is a clear, colourless liquid at room temperature with a characteristic pleasant burning taste and sweet spirituous odour.
• It has a boiling point of 78°C and is highly soluble/miscible in water in all proportions due to hydrogen bonding.

Why used as a medical solvent: Ethanol is a polar covalent organic liquid capable of dissolving a wide range of organic and inorganic compounds that do not dissolve in water. Hence, it is widely used as a solvent in cough syrups, tonics, and tinctures of iodine.

1. Reaction with Sodium metal: Evolving hydrogen gas and forming sodium ethoxide. $$2\text{CH}_3\text{CH}_2\text{OH}(l) + 2\text{Na}(s) \rightarrow 2\text{CH}_3\text{CH}_2\text{ONa}(aq) + \text{H}_2(g)\uparrow$$
2. Reaction with hot concentrated sulphuric acid at 443 K (170°C): Undergoing dehydration to form ethene. $$\text{CH}_3\text{CH}_2\text{OH} \xrightarrow{\text{Hot Conc. } \text{H}_2\text{SO}_4, \text{ 443 K}} \text{CH}_2=\text{CH}_2(g) + \text{H}_2\text{O}(l)$$

Role of concentrated sulphuric acid: It acts as a powerful dehydrating agent, extracting water molecules from the ethanol structure.

Why denatured? To prevent the misuse of cheap industrial-grade ethanol for recreational drinking and to evade heavy liquor taxes.
Substances added: Poisonous substances like methanol ($\text{CH}_3\text{OH}$), pyridine, or copper sulphate (which adds a warning blue colour).

It is a colourless, corrosive liquid with a sharp, pungent, vinegar-like sour smell and sour taste. A 5–8% solution of acetic acid in water is called vinegar.
Glacial Acetic Acid: 100% pure anhydrous ethanoic acid.
Why called so: The melting point of pure ethanoic acid is 17°C (290 K). During cold winter climates, it easily freezes into a crystalline solid that resembles blocks of ice (glaciers). Hence, it is commonly called glacial acetic acid.

Balanced chemical equation: $$\text{CH}_3\text{COOH}(l) \text{ (Ethanoic acid)} + \text{C}_2\text{H}_5\text{OH}(l) \text{ (Ethanol)} \xrightarrow{\text{Conc. } \text{H}_2\text{SO}_4} \text{CH}_3\text{COOC}_2\text{H}_5(aq) \text{ (Ethyl ethanoate)} + \text{H}_2\text{O}(l)$$ Experimental Setup: Mix equal volumes of ethanol and ethanoic acid in a test tube, add a few drops of conc. $\text{H}_2\text{SO}_4$, and heat the test tube in a warm water bath.
Characteristic property: Esters have a highly characteristic, pleasant, sweet-fruity fragrance.

Balanced chemical equation: $$\text{CH}_3\text{COOC}_2\text{H}_5(aq) + \text{NaOH}(aq) \rightarrow \text{CH}_3\text{COONa}(aq) + \text{C}_2\text{H}_5\text{OH}(aq)$$ Relation to soap making: Natural soaps are prepared industrially by this exact saponification reaction. Large molecules of natural esters (fats and oils) are boiled with sodium hydroxide solution, yielding glycerol and the sodium salts of long-chain fatty acids (soap).

1. Reaction with Sodium hydroxide ($\text{NaOH}$): $$\text{CH}_3\text{COOH}(aq) + \text{NaOH}(aq) \rightarrow \text{CH}_3\text{COONa}(aq) + \text{H}_2\text{O}(l)$$
2. Reaction with Sodium carbonate ($\text{Na}_2\text{CO}_3$): $$2\text{CH}_3\text{COOH}(aq) + \text{Na}_2\text{CO}_3(s) \rightarrow 2\text{CH}_3\text{COONa}(aq) + \text{H}_2\text{O}(l) + \text{CO}_2(g)\uparrow$$
3. Reaction with Sodium hydrogen carbonate ($\text{NaHCO}_3$): $$\text{CH}_3\text{COOH}(aq) + \text{NaHCO}_3(s) \rightarrow \text{CH}_3\text{COONa}(aq) + \text{H}_2\text{O}(l) + \text{CO}_2(g)\uparrow$$

Diagnostic Gas Test: The evolved carbon dioxide ($\text{CO}_2$) gas causes rapid effervescence. If passed through lime water [$\text{Ca(OH)}_2$], the lime water turns milky due to the formation of an insoluble white precipitate of calcium carbonate ($\text{CaCO}_3$).

1. Litmus paper test:
   • Ethanoic acid: Being an acid, it immediately turns blue litmus paper red.
   • Ethanol: Being neutral, it does not show any change in colour on blue or red litmus paper.
2. Sodium hydrogen carbonate ($\text{NaHCO}_3$) test:
   • Ethanoic acid: Reacts vigorously to produce rapid effervescence with the evolution of colorless carbon dioxide gas: $$\text{CH}_3\text{COOH} + \text{NaHCO}_3 \rightarrow \text{CH}_3\text{COONa} + \text{H}_2\text{O} + \text{CO}_2\uparrow$$
   • Ethanol: Does not react at all, and no gas bubbles or effervescence are observed.

Chemical Structure:

1. Hydrophilic (ionic) head: The carboxylate end ($-\text{COO}^-\text{Na}^+$). It is highly polar and water-loving (soluble in water, insoluble in grease).
2. Hydrophobic (hydrocarbon) tail: The long, non-polar alkyl chain ($\text{C}_{17}\text{H}_{35}-$). It is non-polar, grease-loving, and water-fearing (soluble in organic oils/grease, insoluble in water).

Why micelle formation occurs: When soap is added to water, the polar, hydrophilic ionic heads are attracted to water molecules and point outwards towards the surrounding water. The non-polar, hydrophobic hydrocarbon tails are repelled by water and align themselves inwards towards the center of the sphere, clustering together to avoid contact with water. This spherical alignment is called a micelle.

1. Wetting: Soap dissolves in water, and the soap molecules orient themselves at the surface, lowering the surface tension of water.
2. Micelle Formation around Dirt: When dirty clothes containing oily grease or dirt are immersed, the hydrophobic tails of the soap molecules dissolve in the oily droplet, while the hydrophilic ionic heads remain dissolved in the surrounding water.
3. Trapping the Dirt: The soap molecules form a spherical micelle structure around the oil droplet, trapping it securely at the core of the sphere.
4. Emulsification and Rinsing: When the water is agitated or rubbed, the hydrophobic tails pull the oil/grease droplet off the fabric surface into the water. The micelles, having negatively charged ionic heads, repel each other and remain suspended as a stable emulsion in water. Rinsing with running water carries these dirt-filled micelles away, leaving the fabric clean.

Scientific Reason: Ethanol is a non-polar organic solvent (unlike highly polar water). The long hydrocarbon tails of the soap molecules are highly soluble in ethanol and have no drive to cluster together inside a sphere. Simultaneously, the polar ionic heads are not attracted to non-polar ethanol and have no drive to face outwards. Therefore, the soap molecules dissolve individually in ethanol as a homogeneous solution without forming any micelle structures.

Salts present: Calcium and Magnesium hydrogencarbonates, chlorides, or sulphates.
Scum formation: When soap is added to hard water, the sodium ions in the soap molecule are displaced by calcium or magnesium ions to form an insoluble, sticky greyish-white precipitate called scum: $$2\text{C}_{17}\text{H}_{35}\text{COONa}(aq) + \text{Ca}^{2+}(aq) \rightarrow (\text{C}_{17}\text{H}_{35}\text{COO})_2\text{Ca}(s)\downarrow \text{ (Scum)} + 2\text{Na}^+(aq)$$ This scum wastes a large amount of soap and sticks to the fabric, making the cleaning action highly ineffective.

Chemical difference: Soaps are sodium salts of weak carboxylic acids ($-\text{COONa}$). Detergents are sodium salts of long-chain benzene sulphonic acids ($-\text{SO}_3\text{Na}$) or alkyl hydrogen sulphates ($-\text{OSO}_3\text{Na}$).
Why effective in hard water: The calcium and magnesium salts of sulphonic acids (unlike those of carboxylic acids) are highly soluble in water. When a detergent is added to hard water, it does not react with calcium and magnesium ions to form insoluble precipitates/scum. It remains in its active molecular form, producing rich lather and cleaning effectively even in hard water.

Advantages:

1. They clean highly effectively in both soft and hard water without forming scum.
2. They can be used in acidic water or highly saline water where soaps are completely deactivated.

Disadvantages (Environmental Impact):

1. Detergents containing highly branched hydrocarbon chains are non-biodegradable. They are not decomposed by soil bacteria, leading to persistent water and soil pollution.
2. They cause heavy foaming in rivers and water bodies, blocking oxygen dissolution and harming aquatic life.

1. Balanced chemical equation: $$\text{C}_2\text{H}_5\text{OH}(l) + 3\text{O}_2(g) \rightarrow 2\text{CO}_2(g) + 3\text{H}_2\text{O}(g) + \text{Heat}$$
2. Why cleaner/eco-friendly: Petrol contains long-chain hydrocarbons that undergo incomplete combustion, releasing toxic carbon monoxide, nitrous oxides, and unburnt carbon soot. Ethanol, having an oxygen atom in its molecule ($\text{C}_2\text{H}_5\text{OH}$), undergoes highly complete combustion, releasing only carbon dioxide and water vapour.
3. Sugarcane solar converter: Sugarcane traps massive amounts of solar energy via photosynthesis, converting it into chemical energy in sugar molecules. Fermenting this sugar yields ethanol, which acts as a liquid solar fuel reserve.

1. Balanced chemical equation: $$\text{CH}_3\text{COOH}(l) + \text{C}_2\text{H}_5\text{OH}(l) \xrightarrow{\text{Conc. } \text{H}_2\text{SO}_4} \text{CH}_3\text{COOC}_2\text{H}_5(aq) + \text{H}_2\text{O}(l)$$ Ester Name: Ethyl ethanoate.
2. Dual role of conc. sulphuric acid:
   • It acts as an acid catalyst, speeding up the reaction.
   • It acts as a dehydrating agent, absorbing water molecules as they are formed. By removing water, it forces the equilibrium of this reversible reaction to shift forward (according to Le Chatelier's principle), maximizing the yield of ester.
3. Why water bath heating: Ethanol is highly flammable and volatile. If heated directly over an open Bunsen burner flame, its vapours could easily ignite, causing a serious lab fire. Heating in a warm water bath ensures safe, uniform temperature control below ethanol's boiling point.

1. Why regular soap fails: Ramesh's groundwater contains dissolved calcium and magnesium ions. When he rubs soap, the sodium soap molecules undergo double displacement to form an insoluble sticky mass instead of lather. This precipitate is called scum.
2. Ionic reactions: $$2\text{C}_{17}\text{H}_{35}\text{COO}^-\text{Na}^+(aq) + \text{Ca}^{2+}(aq) \rightarrow (\text{C}_{17}\text{H}_{35}\text{COO})_2\text{Ca}(s)\downarrow + 2\text{Na}^+(aq)$$ $$2\text{C}_{17}\text{H}_{35}\text{COO}^-\text{Na}^+(aq) + \text{Mg}^{2+}(aq) \rightarrow (\text{C}_{17}\text{H}_{35}\text{COO})_2\text{Mg}(s)\downarrow + 2\text{Na}^+(aq)$$
3. Why shower gel (detergent) works: Shower gels are formulated using synthetic detergents (like sodium lauryl sulphate). Their calcium and magnesium salts are completely soluble in water and do not precipitate as scum. Thus, they lather immediately and clean effectively.

1. General formula of alcohols: $\text{C}_n\text{H}_{2n+1}\text{OH}$.
2. Why boiling point increases: Moving from methanol to butanol, the molecular size and carbon chain length increase. This increases the surface area of the molecule, which significantly strengthens the intermolecular van der Waals forces of attraction between the molecules. Since stronger intermolecular forces require more thermal energy to break, the boiling point increases.
3. Solubility comparison: Methanol has a higher solubility in water than butanol.
   Justification: Alcohols consist of a polar hydrophilic $-\text{OH}$ head (which forms hydrogen bonds with water) and a non-polar hydrophobic alkyl tail. In methanol ($\text{CH}_3-$), the hydrophobic tail is tiny, allowing hydrogen bonding to dominate. In butanol ($\text{C}_4\text{H}_9-$), the large hydrophobic tail repels water, significantly lowering its solubility.

1. Step-by-step substitution of methane: $$\text{CH}_4 + \text{Cl}_2 \xrightarrow{\text{UV Light}} \text{CH}_3\text{Cl} + \text{HCl} \text{ (Chloromethane)}$$ $$\text{CH}_3\text{Cl} + \text{Cl}_2 \xrightarrow{\text{UV Light}} \text{CH}_2\text{Cl}_2 + \text{HCl} \text{ (Dichloromethane)}$$ $$\text{CH}_2\text{Cl}_2 + \text{Cl}_2 \xrightarrow{\text{UV Light}} \text{CHCl}_3 + \text{HCl} \text{ (Trichloromethane / Chloroform)}$$ $$\text{CHCl}_3 + \text{Cl}_2 \xrightarrow{\text{UV Light}} \text{CCl}_4 + \text{HCl} \text{ (Tetrachromethane / Carbon tetrachloride)}$$
2. Why called chain reaction: The reaction is initiated by UV light homolytically cleaving chlorine molecules into chlorine free radicals. These radicals continuously react, regenerating new radicals in each step, maintaining a propagation chain until the reactants are exhausted.
3. Butane molecular formula and isomers:
   • Molecular Formula: $\text{C}_4\text{H}_{10}$
   • Isomers:
     1. n-Butane (straight chain): $\text{CH}_3-\text{CH}_2-\text{CH}_2-\text{CH}_3$
     2. Iso-butane (branched chain): $\text{CH}_3-\text{CH}(\text{CH}_3)-\text{CH}_3$ (2-Methylpropane)

1. Identification of compounds:
   • Compound 'A' is Ethanol ($\text{C}_2\text{H}_5\text{OH}$).
   • Compound 'B' is Ethanoic acid ($\text{CH}_3\text{COOH}$).
   • Compound 'C' is the ester Ethyl ethanoate ($\text{CH}_3\text{COOC}_2\text{H}_5$).
   • Compound 'D' is Sodium acetate ($\text{CH}_3\text{COONa}$).
2. Chemical equations:
   1. A to B (Oxidation): $$\text{CH}_3\text{CH}_2\text{OH}(l) \xrightarrow{\text{Alkaline } \text{KMnO}_4, \Delta} \text{CH}_3\text{COOH}(aq)$$
   2. A + B to C (Esterification): $$\text{CH}_3\text{COOH}(l) + \text{C}_2\text{H}_5\text{OH}(l) \xrightarrow{\text{Conc. } \text{H}_2\text{SO}_4} \text{CH}_3\text{COOC}_2\text{H}_5(aq) + \text{H}_2\text{O}(l)$$
3. Reaction of 'C' with NaOH: $$\text{CH}_3\text{COOC}_2\text{H}_5(aq) + \text{NaOH}(aq) \rightarrow \text{CH}_3\text{COONa}(aq) + \text{C}_2\text{H}_5\text{OH}(aq)$$ This reaction is called Saponification.

When sunlight hits the thin soap film of the bubble, a portion of the light waves is reflected off the outer surface, and another portion penetrates and reflects off the inner surface. Because the film is extremely thin, these two sets of reflected light waves constructively and destructively interfere with each other. Different wavelengths (colours) are cancelled or amplified depending on the film thickness, producing bright, swirling rainbow patterns.

Detailed explanations:

1. Catenation: Carbon atoms can link together through strong, stable C-C single, double, or triple covalent bonds. The small atomic radius of carbon allows the nuclei to attract the shared electrons strongly, producing a very high C-C bond energy (348 kJ/mol). Carbon can form straight chains of infinite length, branches of all shapes, and closed rings.
2. Tetravalency: Having 4 valence electrons, carbon requires 4 more to complete its octet. It can form stable bonds with monovalent atoms (H, Cl, Br) as well as double/triple bonds with polyvalent heteroatoms (O, N, S). This allows carbon to construct complex molecules of diverse structures and functions.

• Coal: Formed over 300 million years ago from the remains of ancient trees and ferns buried under soil. Under high pressure, temperature, and anaerobic conditions, these remains slowly decayed and carbonised to form coal.
• Petroleum: Formed from the remains of microscopic marine organisms that died and sank to the seabed millions of years ago. They were covered by sand and clay. Geological pressure and high temperatures converted these marine lipids and organic matter into oil and natural gas.

Why non-renewable: Their natural formation process takes millions of years under highly specific geological conditions. We are burning these reserves millions of times faster than they can be regenerated, meaning once depleted, they are gone forever.

How it works: The aluminium object is made the anode and electrolysed in a dilute sulphuric acid bath. Oxygen gas evolved at the anode reacts with the aluminium to form a tough oxide film ($\text{Al}_2\text{O}_3$).
Relation to Carbon properties: During industrial smelting of aluminium (Hall-Heroult process), the anode consists of large carbon (graphite) blocks. The oxygen released at the anode reacts with these carbon blocks, eroding them by converting carbon into carbon dioxide gas: $$\text{C}(s) + 2\text{O}^{2-} \rightarrow \text{CO}_2(g) + 4e^-$$ This requires the carbon anodes to be replaced periodically, demonstrating carbon's high reactivity with oxygen at high temperatures.

1. $$\text{CH}_3\text{COOH}(aq) + \text{NaHCO}_3(s) \rightarrow \text{CH}_3\text{COONa}(aq) + \text{H}_2\text{O}(l) + \text{CO}_2(g)\uparrow$$
2. $$2\text{C}_2\text{H}_5\text{OH}(l) + 2\text{Na}(s) \rightarrow 2\text{C}_2\text{H}_5\text{ONa}(aq) + \text{H}_2(g)\uparrow$$
3. $$\text{CH}_3\text{COOC}_2\text{H}_5(aq) + \text{NaOH}(aq) \rightarrow \text{CH}_3\text{COONa}(aq) + \text{C}_2\text{H}_5\text{OH}(aq)$$
4. $$\text{CH}_3\text{CH}_2\text{OH} \xrightarrow{\text{Hot Conc. } \text{H}_2\text{SO}_4, \text{ 443 K}} \text{CH}_2=\text{CH}_2(g) + \text{H}_2\text{O}(l)$$

• Soaps: Sodium or potassium salts of long-chain natural fatty carboxylic acids ($-\text{COONa}$).
  Biodegradability: Since they are derived from natural plant and animal fats, soaps are completely biodegradable. Soil and water bacteria decompose them easily into harmless compounds.
• Detergents: Sodium salts of synthetic benzene sulphonic acids ($-\text{SO}_3\text{Na}$).
  Biodegradability: They are synthetic compounds, often containing branched hydrocarbon chains. They are non-biodegradable, persisting in water bodies and causing severe foam pollution.

1. Charcoal (Carbon): Being a solid fuel with no volatile matter, it does not burn with a flame. It only glows red and releases heat, producing carbon dioxide gas: $$\text{C}(s) + \text{O}_2(g) \rightarrow \text{CO}_2(g)$$ It leaves behind solid ash (inorganic minerals) as residue.
2. Candle (Hydrocarbons): The paraffin wax melts and vaporizes. The volatile hydrocarbons burn with a distinct yellow, luminous flame due to carbon particles glowing inside the flame. The combustion products are carbon dioxide and water vapour: $$\text{Paraffin} + \text{O}_2 \rightarrow \text{CO}_2(g) + \text{H}_2\text{O}(g)$$ It leaves no solid residue if combustion is complete, but can leave a black soot on objects held directly in the flame.

• Covalent bonds are directional: They are formed by the overlap of specific atomic orbitals (like s, p orbitals) in definite spatial directions. The shared electron pairs are concentrated along specific axes, holding the atoms at fixed angles relative to each other.
• Ionic bonds are non-directional: They are held by electrostatic attractions. Oppositely charged ions attract each other equally in all directions, without any spatial constraints or fixed angles.

How this directional property leads to structural isomerism: Because covalent bonds are locked at fixed angles in space, a set of carbon and hydrogen atoms can be arranged in multiple distinct 3D structural geometries (e.g., straight chains, branches, or different functional group placements). Since these directional bonds cannot freely shift without breaking and reforming, each spatial arrangement represents a completely different compound with distinct physical and chemical properties (structural isomers).